Re: [Libguestfs] [PATCH 2/2] build: Replace ./nbdkit with a C program.

Ah, but here, we can rely on the fact that optarg is NULL when there is no option (regardless of whether the option was short or long). (It's trickier if there are any optional_argument entries for has_arg - but since we stick to just no_argument and required_argument, we don't have to worry about that).